1. Field of the Invention
The present invention relates to a valve-driving system for driving an intake valve or an exhaust valve of an internal combustion engine.
2. Description of the Related Art
The intake valve and the exhaust valve of the conventional internal combustion engine are driven to be opened or closed by power taken out from a crankshaft of the internal combustion engine. Recently, however, it has been attempted to drive the intake valve and the exhaust valve by using an electric motor. For example, Japanese Patent Application Laying Open NO. Hei 8-177536 discloses a valve-driving apparatus for driving a camshaft by using a motor to open or close the intake valve.
Moreover, for example, Japanese Patent Application Laying Open NO. Hei 10-169418 discloses an electromagnetically driven valve mechanism for driving a valve body of the intake valve or the exhaust valve by an electromagnetic force, in a variable valve mechanism of the internal combustion engine which is capable of continuously varying an operating angle and a phase of the intake valve or the exhaust valve to control an intake air amount.
However, if the valve body is driven to be opened or closed by the electromagnetically driven valve mechanism, which is disclosed in the above-described Japanese Patent Application Laying Open NO. Hei 10-169418 or the like, or if the valve body is driven to be opened or closed by the rotation of a camshaft by the electric motor independently of the rotation of the crankshaft, which is disclosed in Japanese Patent Application Laying Open NO. Hei 8-177536 or the like, it is necessary to synchronize the valve-driving system with the rotation of the crankshaft, i.e. piston motion, highly accurately, as opposed to the conventional case where the opening or closing of the valve-driving is performed by the power taken out from the crankshaft. If they become out of synchronization greatly by a failure or at the moment of some motions, that possibly not only decreases the performance of the internal combustion engine, but also causes the collision of the valve body and the piston or the collision of the intake valve and the exhaust valve, consequently damaging the internal combustion engine, which is a technical problem.
On the other hand, in order to prevent this problem, it is also conceivable to design to provide a recess or escape portion or the like at the upper portion of the piston so as not to contact the valve body with the piston even in the largest lift condition. However, this is restricted in design in many cases by the shape of a combustion chamber. Even if the above design is realized, there is a technical problem that it is difficult to ensure a high compression ratio required for a diesel engine or the like.